As technologies for generating desired gaits of a mobile robot, such as a bipedal mobile robot, there have been known technologies in which an error of a floor reaction force moment about a desired ZMP or an error of an actual ZMP from the desired ZMP is observed and a gait is corrected to reduce the error, as disclosed in, for example, Japanese Patent No. 3443077 (patent document 1) or in “Real-time walking stabilization control of a biped humanoid robot—Verifying the validity of a walking control module in HRP—”/3P14/The 18th Annual Conference of the Robotics Society of Japan (non-patent document 1).
However, these technologies do not consider an error of a translational floor reaction force; therefore, if a gait is to be generated for a robot to walk on a road surface having a low friction coefficient or if a gait having a period during which a translational floor reaction force vertical component becomes zero or substantially zero, such as in running, is to be generated, it will be difficult to generate a gait that restrains the robot from slipping.
Thus, technologies disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2002-326173 (patent document 2) and PCT international publication WO/03/057427/A1 (patent document 3) have been proposed by the present applicant. According to the technologies disclosed in these patent documents 2 and 3, an instantaneous desired gait composed of an instantaneous value of a desired motion (instantaneous desired motion) of a robot and an instantaneous value of a desired floor reaction force (instantaneous desired floor reaction force) is sequentially created using a first dynamic model (simplified model), which represents a relationship between motions of the robot (the positions and postures of individual portions) and floor reaction forces, such that a dynamic balance condition (a condition, such as the one in that a translational force component of a floor reaction force takes a desired value or a floor reaction force moment about a certain point takes a desired value) on the first dynamic model is satisfied. Then, the instantaneous desired gait is input to a second dynamic model (full model) wherein a part of the instantaneous desired motion (desired body position/posture, a desired moment about a desired ZMP, or the like) is corrected so as to generate a final instantaneous desired gait in a time series manner.
According to the technology, using a model having high linearity as the first dynamic model (simplified model) makes it possible to efficiently and promptly create a gait that enables a robot to continue a stable motion, and using a model having relatively high dynamic accuracy as a second dynamic model (full model) makes it possible to bring the dynamic accuracy between a motion of a finally generated gait and a floor reaction force closer to the dynamics of an actual robot.
However, in the technologies disclosed in the aforesaid patent documents 2 and 3, gaits created using the second dynamic model tend to diverge, so that it has been necessary to correct a desired ZMP trajectory or generate a floor reaction force moment about a desired ZMP so as to restrain a desired motion trajectory of a robot from deviating from a gait created using the first dynamic model. And, in this case, the correction amount of the desired ZMP trajectory or the floor reaction force moment about the desired ZMP has occasionally become relatively large, and in such a case, it has become difficult to maintain an ample stability margin from time to time. Conversely, if the correction amount of the desired ZMP trajectory or the permissible range of the floor reaction force moment about the desired ZMP is set to be smaller in order to maintain an ample stability margin, then the likelihood of the divergence of a gait has inconveniently increased.
The present invention has been made with a view of the above background, and it is an object thereof to provide a gait generating system for a mobile robot that is capable of efficiently generating a gait that allows a permissible range of a predetermined component of a floor reaction force set for preventing slippage or the like of a robot to be satisfied and also capable of securing high dynamic accuracy between a motion and a floor reaction force of the gait.